BMW M40B18 Engine

  1. Specifications
  2. Overview, problems
  3. Performance tuning

M40B18 Specs

Manufacturer Steyr Plant
Also called BMW M40
Production 1987-1994
Cylinder block alloy Cast iron
Configuration Straight-4
Valvetrain SOHC
2 valves per cylinder
Piston stroke, mm (inch) 81 (3.19)
Cylinder bore, mm (inch) 84 (3.3)
Compression ratio 9
Displacement 1796 cc (109.6 cu in)
Power output 83 kW (113 HP) at 5,500 rpm
Torque output 162 Nm (119 lb·ft) at 4,250 rpm
Redline 6,200 rpm
HP per liter 62.7
Fuel type Gasoline
Fuel system Bosch Motronic 1.3 (E30)
Bosch Motronic 1.7 (E36)
Weight, kg (lbs) ~132 (290)
Fuel consumption, L/100 km (mpg)

for E30 318i
10.3 (22.8)
6.7 (35.1)

8.6 (27.4)
Turbocharger Naturally aspirated
Oil consumption , L/1000 km
(qt. per miles)
up to 1.0
(1 qt. per 750 miles)
Recommended engine oil 0W-30
Engine oil capacity, L (qt.) 4.0 (4.2)
Oil change interval, km (miles) 7,000-10,000
Normal engine operating temperature, °C (F) 90-95 (195-203)
Engine lifespan, km (miles)
-Official information

300+ (185)
Tuning, HP
-Max HP
-No life span loss


The engine is installed in BMW 318i E30
BMW 318i E36
BMW 518i E34

BMW M40B18 engine reliability, problems and repair

M40B18 also belongs to BMW M40 series and it is an elder brother of M40B16 engine. It was developed in 1987 as replacement of older M10 series that was already out-of-date at that time. This motor is based on cast-iron cylinder block, 8-valve cylinder head with one camshaft and hydraulic lifters. Valve adjustment is not necessary for M40B18. Diameter of inlet valves is 42 mm while outlet valves are 36 mm in diameter. BMW M40 camshaft specs are as follows: duration 244/244 deg, lift 10.6/10.6 mm.
Engine is equipped with unreliable timing belt which calls for regular checking and control. Replacement of the belt is necessary every 25,000 miles (40,000 km) of mileage. Drivers should take this problem rather seriously otherwise belt break down can lead to bended valves.
This engine was mainly used for BMW 18i models.
Along with M40B18 engine production of more powerful 1.8-liter version of M42B18 was launched in 1989. This motor could be found under the bonnet of sports models including 18i/18is/18ti.
New version of 4-cylinder 1.8-liter BMW M43B18 engine was firstly introduced in 1992 and replaced older motor within two years.

BMW M40 disadvantages and problems

1. Engine knocking. As a rule M40 engines are rather noisy. This is due camshaft and hydraulic tappets wear out. That is why it is necessary to check conditions of camshaft regularly. In case you see any notice of wearing off, this detail must be replaced as soon as possible.
2. Rough idle. Air flow sensor must also be checked. It may be damaged after some time which can result in air leaking.
Next you need to have your air flow sensor and oxygen sensor checked. Also pay attention to conditions of the throttle body and idling valve. Another problem of uneven idling can be connected with difficult rotating of camshaft.
3. Acceleration problems. The main reason for such problem is related to polluted injectors. If you clean them, the problem will be gone.
4. Overheating. First of all you need to examine your radiator in case such problem occurs. Don’t forget to check water pump and thermostat. Also pay attention to conditions of plastic pipes which are part of the cooling system.
5. M40 is unable to start. You can find the reason of this problem in fuel pump, spark plugs, high-voltage wires and ignition coil.
BMW M40 engine has already proved to be rather unreliable. Its lifespan is about 180,000 miles (300,000 km) of mileage. In some occasions it can be a little higher. Nevertheless the majority of BMW M40B18 engines have already used their lifespan and nothing can be said about their reliability and usage.
Is BMW M40B18 really worth buying? No, it isn’t. You’d better purchase BMW M50 or M54. These engines are much better and have higher level of reliability.

BMW M40B18 engine tuning

Chip tuning. Stroker

M40B18 engine is equal to M40B16 when it comes to tuning and different mods. HERE you can find out how to increase HP of BMW M40.

BMW M40B18 Turbo

Before you start spending thousands of dollars for turbo tuning of M40 you need to have clear understanding that it would be better to and less expensive to purchase BMW M50B25 or M54B30. These engines have higher level of reliability and margin of safety to proceed with modifications.
BMW M40 can cope with turbocharging rather well. Stock internals are enough to deal with over 19 psi (1.3 bar) boost due to thick cylinder head gasket and ARP studs. If you want to increase engine power you need to buy TD04 turbocharger or any other equal to it, weld turbo manifold, purchase intercooler, blow-off, wastegate, install oil feed line and oil return line. Moreover you will additionally need fuel pressure regulator, Walbro 255 lph fuel pump, boost controller, 550 or 630 cc injectors, 2.5-inch piping and 2.5-inch exhaust system.
You can build something equal on base of Eaton M45 supercharger.